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NIR Transmission Gratings

  • Gratings Designed for Optimum Use in the NIR
  • Two Groove Angles Available: 24.8° and 31.7°
  • Two Sizes Available: 25 mm x 25 mm and 50 mm x 50 mm


(50 mm x 50 mm)


(25 mm x 25 mm)

Related Items

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Selection Guide
Reflective Gratings
Ruled UV
Near IR
Mid IR
Transmission Gratings
Near IR
Common Specifications
Substrate Material Schott B270
Thickness 3 mm Nominal
Dimensional Tolerances ±0.5 mm
Thickness Tolerance ±0.5 mm


  • Designed for Optimum Performance in the Near Infrared
  • Ideal for Fixed Grating Applications
  • Schott B270 Substrate
  • Custom Sizes Available Upon Request

Thorlabs' Near Infrared Transmission Gratings are designed for the 500 nm to 1.8 μm range. Due to their basic simplicity, transmission gratings are beneficial for use in fixed grating applications, such as spectrographs. The incident light is dispersed on the opposite side of the grating at a fixed angle. Transmission gratings provide low alignment sensitivity, which minimizes alignment errors. These grooved transmission gratings were designed for optimum performance in the near infrared, offering different levels of dispersion. In most cases, the efficiency of these gratings is comparable to that of reflection gratings such as Ruled Gratings or Holographic Gratings when used in the same wavelength range.

By necessity, transmission gratings require relatively coarse groove spacings to maintain high efficiency. As the diffraction angles increase with the finer spacings, the refractive properties of the substrate materials used limit the transmission at the higher wavelengths and performance drops off. The grating dispersion characteristics, however, lend themselves to compact systems utilizing small detector arrays. The gratings are also relatively polarization insensitive. Our NIR transmission gratings are offered in two different sizes, with a choice of two groove angles. Please see the graph to the right for performance characteristics.

Please see the Gratings Guide tab to choose the right grating for your application.

Mounts and Adapters

Thorlabs' gratings can be mounted directly into the KM100C Right-Handed or KM100CL Left-Handed Kinematic Rectangular Optic Mount for precise and stable mounting and alignment.


Optical gratings can be easily damaged by moisture, fingerprints, aerosols, or the slightest contact with any abrasive material. Gratings should only be handled when necessary and always held by the sides. Latex gloves or a similar protective covering should be worn to prevent oil from fingers from reaching the grating surface. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen. Solvents will likely damage the grating's surface.

Thorlabs uses a clean room facility for assembly of gratings into mechanical setups. If your application requires integrating the grating into a sub-assembly or a setup, please contact us to learn more about our assembly capabilities.

The absolute efficiency plotted here includes Fresnel reflections.
Click Here for Raw Data

Grating Arrows
Click to Enlarge

Top Image: On one edge of the grating, an arrow parallel to the grating's surface indicates the blaze direction.
Bottom Image: On the opposite edge of the grating, an arrow perpendicular to the grating's surface indicates the transmission direction.

Diffraction Gratings Tutorial

Diffraction gratings, either transmissive or reflective, can separate different wavelengths of light using a repetitive structure embedded within the grating. The structure affects the amplitude and/or phase of the incident wave, causing interference in the output wave. In the transmissive case, the repetitive structure can be thought of as many tightly spaced, thin slits. Solving for the irradiance as a function wavelength and position of this multi-slit situation, we get a general expression that can be applied to all diffractive gratings when = 0°,

Grating Equation 1


known as the grating equation. The equation states that a diffraction grating with spacing a will deflect light at discrete angles (theta sub m), dependent upon the value λ, where  is the order of principal maxima. The diffracted angle, theta sub m, is the output angle as measured from the surface normal of the diffraction grating. It is easily observed from Eq. 1 that for a given order m, different wavelengths of light will exit the grating at different angles. For white light sources, this corresponds to a continuous, angle-dependent spectrum.


Transmission Grating
Figure 1. Transmission Grating

Transmission Gratings

One popular style of grating is the transmission grating. This type of diffraction grating is created by scratching or etching a transparent substrate with a repetitive, parallel structure. This structure creates areas where light can scatter. A sample transmission grating is shown in Figure 1.

The transmission grating, shown in Figure 1, is comprised of a repetitive series of narrow-width grooves separated by distance a. The incident light impinges on the grating at an angle theta sub i, as measured from the surface normal. The light of order m exiting the grating leaves at an angle of theta sub m, relative to the surface normal. Utilizing some geometric conversions and the general grating expression (Eq. 1) an expression for the transmissive diffraction grating can be found:

Grating Equation 2


where both  and  are positive if the incident and diffracted beams are on opposite sides of the grating surface normal, as illustrated in the example in Figure 1. If they are on the same side of the grating normal,  must then be considered negative.


Reflective Grating
Figure 2. Reflective Grating

Reflective Gratings

Another very common diffractive optic is the reflective grating. A reflective grating is traditionally made by depositing a metallic coating on an optic and ruling parallel grooves in the surface. Reflective gratings can also be made of epoxy and/or plastic imprints from a master copy. In all cases, light is reflected off of the ruled surface at different angles corresponding to different orders and wavelengths. An example of a reflective grating is shown in Figure 2. Using a similar geometric setup as above, the grating equation for reflective gratings can be found:

Grating Equation 3


where is positive and is negative if the incident and diffracted beams are on opposite sides of the grating surface normal, as illustrated in the example in Figure 2. If the beams are on the same side of the grating normal, then both angles are considered positive.

Both the reflective and transmission gratings suffer from the fact that the zeroth order mode contains no diffraction pattern and appears as a surface reflection or transmission, respectively. Solving Eq. 2 for this condition, theta sub i = theta sub m, we find the only solution to be m=0, independent of wavelength or diffraction grating spacing. At this condition, no wavelength-dependent information can be obtained, and all the light is lost to surface reflection or transmission.

This issue can be resolved by creating a repeating surface pattern, which produces a different surface reflection geometry. Diffraction gratings of this type are commonly referred to as blazed (or ruled) gratings. An example of this repeating surface structure is shown in Figure 3.


Blazed (Ruled) Gratings

Blazed Grating
Figure 4. Blazed Grating, 0th Order Reflection
Blazed Grating
Figure 3. Blazed Grating Geometry

The blazed grating, also known as the echelette grating, is a specific form of reflective or transmission diffraction grating designed to produce the maximum grating efficiency in a specific diffraction order. This means that the majority of the optical power will be in the designed diffraction order while minimizing power lost to other orders (particularly the zeroth). Due to this design, a blazed grating operates at a specific wavelength, known as the blaze wavelength.

The blaze wavelength is one of the three main characteristics of the blazed grating. The other two, shown in Figure 3, are a, the groove or facet spacing, and gamma, the blaze angle. The blaze angle gamma is the angle between the surface structure and the surface parallel. It is also the angle between the surface normal and the facet normal.

The blazed grating features geometries similar to the transmission and reflection gratings discussed thus far; the incident angle () and th order reflection angles () are determined from the surface normal of the grating. However, the significant difference is the specular reflection geometry is dependent on the blaze angle, gamma, and NOT the grating surface normal. This results in the ability to change the diffraction efficiency by only changing the blaze angle of the diffraction grating.

The 0th order reflection from a blazed grating is shown in Figure 4. The incident light at angle theta sub i is reflected at theta sub m for m = 0. From Eq. 3, the only solution is theta sub i = –theta sub m. This is analogous to specular reflection from a flat surface.

Blazed Grating
Figure 6. Blazed Grating, Incident Light Normal to Grating Surface
Blazed Grating
Figure 5. Blazed Grating, Specular Reflection from Facet

The specular reflection from the blazed grating is different from the flat surface due to the surface structure, as shown in Figure 5. The specular reflection, theta sub r, from a blazed grating occurs at the blaze angle geometry. This angle is defined as being negative if it is on the same side of the grating surface normal as theta sub i. Performing some simple geometric conversions, one finds that

Grating Equation 2


Figure 6 illustrates the specific case where theta sub i= 0°, hence the incident light beam is perpendicular to the grating surface. In this case, the 0th order reflection also lies at 0°. Utilizing Eqs. 3 and 4, we can find the grating equation at twice the blaze angle:

Grating Equation 2


Littrow Configuration

The Littrow configuration refers to a specific geometry for blazed gratings and plays an important role in monochromators and spectrometers. It is the angle  at which the grating efficiency is the highest. In this configuration, the angle of incidence of the incoming and diffracted light are the same, theta sub i = theta sub m, and m > 0 so

Grating Equation 2


Blazed Grating
Figure 7. Littrow Configuration

The Littrow configuration angle, Theta sub L, is dependent on the most intense order (m = 1), the design wavelength, lambda sub D, and the grating spacing a. It is easily shown that the Littrow configuration angle, Theta sub L, is equal to the blaze angle, gamma, at the design wavelength. The Littrow / blaze angles for all Thorlabs' Blazed Gratings can be found in the grating specs tables.

Grating Equation 2


It is easily observed that the wavelength dependent angular separation increases as the diffracted order increases for light of normal incidence (for theta sub i= 0°, theta sub m increases as m increases). There are two main drawbacks for using a higher order diffraction pattern over a low order one: (1) a decrease in efficiency at higher orders and (2) a decrease in the free spectral range, Free Spectral Range, defined as:

Grating Equation 2



where lambda is the central wavelength, and m is the order.

The first issue with using higher order diffraction patterns is solved by using an Echelle grating, which is a special type of ruled diffraction grating with an extremely high blaze angle and relatively low groove density. The high blaze angle is well suited for concentrating the energy in the higher order diffraction modes. The second issue is solved by using another optical element: grating, dispersive prism, or other dispersive optic, to sort the wavelengths/orders after the Echelle grating.


Holographic Gratings
Figure 8. Holographic Grating

Holographic Surface Gratings

While blazed gratings offer extremely high efficiencies at the design wavelength, they suffer from periodic errors, such as ghosting, and relatively high amounts of scattered light, which could negatively affect sensitive measurements. Holographic gratings are designed specially to reduce or eliminate these errors. The drawback of holographic gratings compared to blazed gratings is reduced efficiency.

Holographic gratings are made from master gratings by similar processes to the ruled grating. The master holographic gratings are typically made by exposing photosensitive material to two interfering laser beams. The interference pattern is exposed in a periodic pattern on the surface, which can then be physically or chemically treated to expose a sinusoidal surface pattern. An example of a holographic grating is shown in Figure 8.

Please note that dispersion is based solely on the number of grooves per mm and not the shape of the grooves. Hence, the same grating equation can be used to calculate angles for holographic as well as ruled blazed gratings.

Thorlabs offers 4 types of Diffraction Gratings:

Reflective Gratings
Ruled UV Ruled gratings can achieve higher efficiencies than holographic gratings due to their blaze angles. They are ideal for applications centered near the blaze wavelength. Thorlabs offers replicated ruled diffraction gratings in a variety of sizes and blaze angles.
Near IR
Mid IR
Holographic Holographic gratings have a low occurrence of periodic errors, which results in limited ghosting, unlike ruled gratings. The low stray light of these gratings makes them ideal for applications where the signal-to-noise ratio is critical, such as Raman Spectroscopy.
Echelle Echelle gratings are low period gratings designed for use in high diffraction orders. They are generally used with a second grating or prism to separate overlapping diffracted orders. They are ideal for applications such as high-resolution spectroscopy.
Transmission Gratings
UV Thorlabs' transmission gratings disperse incident light on the opposite side of the grating at a fixed angle. They are ruled and blazed for optimum efficiency in their respective wavelength range, are relatively polarization insensitive, and have an efficiency comparable to that of a reflection grating optimized for the same wavelength. They are ideal for applications that require fixed gratings such as spectrographs.
Near IR

Selecting a grating requires consideration of a number of factors, some of which are listed below:

Ruled gratings generally have a higher efficiency than holographic gratings. However, holographic gratings tend to have less efficiency variation across their surface due to how the grooves are made. The efficiency of ruled gratings may be desirable in applications such as fluorescence excitation and other radiation-induced reactions.

Blaze Wavelength:
Ruled gratings have a sawtooth groove profile created by sequentially etching the surface of the grating substrate. As a result, they have a sharp peak around their blaze wavelength. Holographic gratings are harder to blaze, and tend to have a sinusoidal groove profile resulting in a less intense peak around the design wavelength. Applications centered around a narrow wavelength range could benefit from a ruled grating blazed at that wavelength.

Wavelength Range:
Groove spacing determines the optimum spectral range a grating covers and is the same for ruled and holographic gratings having the same grating constant. As a rule of thumb, the first order efficiency of a grating decreases by 50% at 0.66λB and 1.5λB, where λB is the blaze wavelength. Note: No grating can diffract a wavelength greater than 2 times the groove period.

Stray Light:
Due to a difference in how the grooves are made, holographic gratings have less stray light than ruled gratings. The grooves on a ruled grating are machined one at a time which results in a higher frequency of errors. Holographic grooves are made all at once which results in a grating that is virtually free of errors. Applications such as Raman spectroscopy, where signal-to-noise is critical, can benefit from the limited stray light of the holographic grating.

Resolving Power:
The resolving power of a grating is a measure of its ability to spatially separate two wavelengths. It is determined by applying the Rayleigh criteria to the diffraction maxima; two wavelengths are resolvable when the maxima of one wavelength coincides with the minima of the second wavelength. The chromatic resolving power (R) is defined by R = λ/Δλ = n*N, where Δλ is the resolvable wavelength difference, n is the diffraction order, and N is the number of grooves illuminated.

For further information about gratings and selecting the grating right for your application, please visit our Gratings Tutorial.


The surface of a diffraction grating can be easily damaged by fingerprints, aerosols, moisture or the slightest contact with any abrasive material. Gratings should only be handled when necessary and always held by the sides. Latex gloves or a similar protective covering should be worn to prevent oil from fingers from reaching the grating surface. Solvents will likely damage the grating's surface. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen. Scratches or other minor cosmetic imperfections on the surface of a grating do not usually affect performance and are not considered defects.

Posted Comments:
hmardanpur  (posted 2017-07-29 14:19:02.01)
Dear support team, I bought a GTI25-03 NIR grating from thorlabs. I can not find the exact equation for using Transmission Gratings with grove 24.8 deg in the website. Should I use: "a.sin(theta) = m.L" where a=grove density, m=order, L= wavelength, theta= diffraction angle? The tutorial explains the reflective gratings with blazed angles clearly but Transmission is not clear. Second question: should I use incident light as normal (90 deg) to back side of grating or should I use blaze angle as incident angle? I look forward to hearing from you soon. Your Sincerely Hossein Mardanpour
tfrisch  (posted 2017-09-12 01:23:19.0)
Hello, thank you for contacting Thorlabs. In the general case, you can use equation (2) from the Gratings Tutorial to characterize light transmitted through a grating. The angle given is the blaze angle which is used when operating in the Littrow configuration which maximizes m=1 efficiency. Blaze angle is equal to the angle of incidence in this special configuration. I will reach out to you directly to discuss your application.
afardad  (posted 2014-04-15 13:11:57.74)
Hi there, I am wondering if you make costume design transmission grating? I need some at 871nm with >1500lines/mm. please notify me via e-mail. Thanks.
pbui  (posted 2014-05-01 04:24:17.0)
We will contact you directly to find out more about your application and requirements to see if we can provide a custom solution.
scottie730318  (posted 2013-03-31 04:10:28.183)
Dear Sir: The absolute efficiency of the GTI NIR transmission grating at the overview page is different to the Catalog.pdf file in the website ( In the overview (, the blue line is the GTIxx-03 (24.8° Blaze Angle), but the Catalog.pdf file show the blue line is the GTIxx-03A. Can you tell me which is correct? Thank you very much.
sharrell  (posted 2013-04-02 09:35:00.0)
Response from Sean at Thorlabs: Thank you for pointing out the inconsistency. The plot on our catalog page was correct. We have updated the plots on our webpage for correctness and clarity.
jjurado  (posted 2011-05-09 10:39:00.0)
Response from Javier at Thorlabs to Mutsuo Ogura: Thank you very much for contacting us. We will contact you directly in order to assist you with your application.
ogura-m  (posted 2011-05-08 22:18:28.0)
Dear sirs, I would like to make a spectrometer between 0.8 and 1.5 micron using NIR Transmission Gratings. The line sensor has a width of about 10mm Will you give any related optical configulation? Sincerely, Mutsuo Ogura, AIST Japan

24.8° Groove Angle NIR Transmission Gratings

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
GTI25-03 Support Documentation
GTI25-03NIR Transmission Grating, 300 Grooves/mm, 24.8° Groove Angle, 25 mm x 25 mm
GTI50-03 Support Documentation
GTI50-03NIR Transmission Grating, 300 Grooves/mm, 24.8° Groove Angle, 50 mm x 50 mm

31.7° Groove Angle NIR Transmission Gratings

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
GTI25-03A Support Documentation
GTI25-03ANIR Transmission Grating, 300 Grooves/mm, 31.7° Groove Angle, 25 mm x 25 mm
GTI50-03A Support Documentation
GTI50-03ANIR Transmission Grating, 300 Grooves/mm, 31.7° Groove Angle, 50 mm x 50 mm
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